device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
INFO: task syz-executor0:16398 blocked for more than 120 seconds.
      Not tainted 4.9.99-gc2f9bce #22
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D29696 16398  12389 0x00000004
 ffff8801d840b000 0000000000000000 ffff88018b34df80 ffffffff84629800
 ffff8801db221b98 ffff8801bda8fb08 ffffffff839e377d ffffffff81233817
 0000000000000000 ffff8801d840b8c0 0000000600000007 ffff8801db222468
Call Trace:
 [<ffffffff839e4d7f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839f03b8>] __rwsem_down_write_failed_common kernel/locking/rwsem-xadd.c:526 [inline]
 [<ffffffff839f03b8>] rwsem_down_write_failed+0x598/0x990 kernel/locking/rwsem-xadd.c:555
 [<ffffffff81ee51e7>] call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:105
 [<ffffffff8122a440>] __down_write arch/x86/include/asm/rwsem.h:125 [inline]
 [<ffffffff8122a440>] down_write_nested+0x60/0xa0 kernel/locking/rwsem.c:174
 [<ffffffff815a7d53>] inode_lock_nested include/linux/fs.h:801 [inline]
 [<ffffffff815a7d53>] do_rmdir+0x293/0x3f0 fs/namei.c:3939
 [<ffffffff815aa02b>] SYSC_unlinkat fs/namei.c:4121 [inline]
 [<ffffffff815aa02b>] SyS_unlinkat+0x5b/0x80 fs/namei.c:4115
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4653>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423bc0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/3683:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d567c>] __fdget_pos+0xac/0xd0 fs/file.c:781
2 locks held by getty/3779:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f2822>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8211cc32>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
2 locks held by syz-executor0/16398:
 #0:  (sb_writers#21){.+.+.+}, at: [<ffffffff815ddf1f>] sb_start_write include/linux/fs.h:1573 [inline]
 #0:  (sb_writers#21){.+.+.+}, at: [<ffffffff815ddf1f>] mnt_want_write+0x3f/0xb0 fs/namespace.c:391
 #1:  (&sb->s_type->i_mutex_key#25/1){+.+...}, at: [<ffffffff815a7d53>] inode_lock_nested include/linux/fs.h:801 [inline]
 #1:  (&sb->s_type->i_mutex_key#25/1){+.+...}, at: [<ffffffff815a7d53>] do_rmdir+0x293/0x3f0 fs/namei.c:3939

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.99-gc2f9bce #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8affd08 ffffffff81eb0f09 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7da0 ffff8801d8affd40
 ffffffff81ebc207 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb0f09>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb0f09>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebc207>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebc19a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7ea4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364c84>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364c84>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364c84>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364c84>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f481c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 16392 Comm: syz-executor0 Not tainted 4.9.99-gc2f9bce #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d7d71800 task.stack: ffff88018b000000
RIP: 0010:[<ffffffff8214d58b>] 
c [<ffffffff8214d58b>] inb arch/x86/include/asm/io.h:316 [inline]
RIP: 0010:[<ffffffff8214d58b>] 
c [<ffffffff8214d58b>] io_serial_in+0x6b/0x90 drivers/tty/serial/8250/8250_port.c:414
RSP: 0018:ffff88018b006f30  EFLAGS: 00000002
RAX: dffffc0000000000 RBX: 00000000000003fd RCX: 0000000000000000
RDX: 00000000000003fd RSI: ffffffff8214d531 RDI: ffffffff864aae78
RBP: ffff88018b006f40 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff864aae40
R13: 0000000000000020 R14: fffffbfff0c9560f R15: fffffbfff0c955d1
FS:  00007fa62f077700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000214a000 CR3: 000000018ae97000 CR4: 00000000001606f0
DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffffffff864aae40
c 000000000000270c
c ffff88018b006f90
c ffffffff8214f154
c
 ffffffff81edc1f8
c ffffffff864aae88
c ffffffff864ab07a
c ffffffff864aae40
c
 000000000000006f
c ffffffff8214f2a0
c dffffc0000000000
c 000000000000006f
c
Call Trace:
 [<ffffffff8214f154>] serial_in drivers/tty/serial/8250/8250.h:111 [inline]
 [<ffffffff8214f154>] wait_for_xmitr+0x94/0x1e0 drivers/tty/serial/8250/8250_port.c:1997
 [<ffffffff8214f2bf>] serial8250_console_putchar+0x1f/0x60 drivers/tty/serial/8250/8250_port.c:3103
 [<ffffffff82137ae9>] uart_console_write+0x59/0xf0 drivers/tty/serial/serial_core.c:1859
 [<ffffffff8215b4c8>] serial8250_console_write+0x528/0x820 drivers/tty/serial/8250/8250_port.c:3169
 [<ffffffff8214803f>] univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:594
 [<ffffffff81259e7d>] call_console_drivers.isra.18.constprop.28+0x1ad/0x360 kernel/printk/printk.c:1589
 [<ffffffff8125cc7f>] console_unlock+0x42f/0xb40 kernel/printk/printk.c:2449
 [<ffffffff8125d7d8>] vprintk_emit+0x448/0x790 kernel/printk/printk.c:1903
 [<ffffffff8125db48>] vprintk+0x28/0x30 kernel/printk/printk.c:1913
 [<ffffffff8125db6d>] vprintk_default+0x1d/0x30 kernel/printk/printk.c:1914
 [<ffffffff8142a995>] vprintk_func kernel/printk/internal.h:36 [inline]
 [<ffffffff8142a995>] printk+0xaf/0xd7 kernel/printk/printk.c:1975
 [<ffffffff81cb748a>] __find_get_block_slow.cold.57+0x37/0xf0 fs/buffer.c:238
 [<ffffffff81621a5e>] __find_get_block+0x23e/0x4c0 fs/buffer.c:1360
 [<ffffffff81622869>] __getblk_slow fs/buffer.c:1101 [inline]
 [<ffffffff81622869>] __getblk_gfp+0x189/0x710 fs/buffer.c:1386
 [<ffffffff8162620d>] __bread_gfp+0x2d/0x270 fs/buffer.c:1420
 [<ffffffff818b3f88>] sb_bread include/linux/buffer_head.h:300 [inline]
 [<ffffffff818b3f88>] fat__get_entry+0x4c8/0x8f0 fs/fat/dir.c:100
 [<ffffffff818b6c11>] fat_get_entry fs/fat/dir.c:128 [inline]
 [<ffffffff818b6c11>] fat_get_short_entry+0x131/0x2a0 fs/fat/dir.c:876
 [<ffffffff818b716d>] fat_scan+0xfd/0x340 fs/fat/dir.c:961
 [<ffffffff818de779>] msdos_find+0xf9/0x2d0 fs/fat/namei_msdos.c:128
 [<ffffffff818df095>] msdos_lookup+0x135/0x250 fs/fat/namei_msdos.c:208
 [<ffffffff815988bd>] lookup_open+0x63d/0x1930 fs/namei.c:3203
 [<ffffffff815a2e33>] do_last fs/namei.c:3315 [inline]
 [<ffffffff815a2e33>] path_openat+0x1803/0x3590 fs/namei.c:3534
 [<ffffffff815a8e87>] do_filp_open+0x197/0x270 fs/namei.c:3568
 [<ffffffff8156b65d>] do_sys_open+0x30d/0x5c0 fs/open.c:1072
 [<ffffffff8156b980>] SYSC_openat fs/open.c:1099 [inline]
 [<ffffffff8156b980>] SyS_openat+0x30/0x40 fs/open.c:1093
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f4653>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 
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